(1) Field of the Invention
The present invention relates to the fabrication of semiconductor structures, and more particularly, to a method of fabricating capacitor structures with very narrow features using silylated photoresist.
(2) Description of the Prior Art
As the feature size of DRAM memory cells continues to decrease, the area available for cell storage capacitors also decreases. Because of these trends it is essential that the capacitance per unit area of the cell capacitor structures is increased. One means of increasing the capacitance is to use special three-dimensional structures such as cylinders and crowns for the capacitors. However, fabricating these structures requires the ability to create very small line widths and spacings. The resolution of the photolithographic and etch processes limits the minimum size of such geometric features. To create very small line and space features for DRAM capacitors that exceed the limits of current processing, an alternative method of patterning and etching the photoresist mask is proposed.
The use of both cylinder and crown capacitor structures is demonstrated in the prior art. U.S. Pat. No. 5,759,893 to Wu teaches a process to make a rugged crown shaped capacitor using doped and undoped polysilicon and hot phosphoric acid etching. U.S. Pat. No. 5,712,202 to Liaw et al teaches a process to make a crown shaped polysilicon capacitor using multiple sidewall spacers and multiple etch back steps. U.S. Pat. No. 5,663,093 to Tseng et al shows the fabrication of a crown shaped polysilicon capacitor using multiple dielectric depositions and etch back steps. U.S. Pat. No. 5,759,892 to Wang et al teaches a method to form self-aligned cylindrical polysilicon capacitors by depositing and etching back several layers of polysilicon.
The use of silylated photoresist in the process of making a DRAM capacitor is also disclosed in the prior art. U.S. Pat. No. 5,753,419 to Misium teaches a method to form a capacitor structure where silylation and etching of photoresist is used to first form wavy vertical etches in the photoresist. An etch of the polysilicon then transfers the wavy pattern to the polysilicon capacitor. U.S. Pat. No. 5,753,420 to Misium teaches a method to form capacitors where silylation of photoresist and dry etching is used to form a top photoresist surface with remnants of photoresist residue. This residue is used as a mask to etch a ripple pattern on the top surface of the polysilicon.